The tenth anniversary of 9/11

A national moment of remembrance will take place at noon on Sunday to mark the tenth anniversary of the Sept. 11, 2001 terrorist attacks. Staff and users who wish to remember and honor those affected by the tragedies are encouraged to pause for one minute of reflection, or to visit a local memorial event.

Special Announcement

Construction detour

Road D and the bike path along Road D between Road B and the east IB/CDF intersection are closed to all traffic. This means there should not be any vehicles, bikes or pedestrians, including local traffic, traveling to and between CDF & the Industrial Buildings via Road D (except Fire Department), for any reason. Alternate routes have been established and marked. Road D can be crossed at the intersection with Road B and at the intersection east of IB/CDF. FESS appreciates your cooperation.

CERN, Ars Electronica introduce artist-in-residency program

Scientists from dozens of countries and cultures mingle at CERN, home to the Large Hadron Collider. Last weekend, the laboratory announced plans to introduce a new element into the mix: artists.

CERN and international cyberarts organization Ars Electronica will partner for the next three years to offer one part of CERN’s new multidisciplinary artist-in-residency program, Collide@CERN. They announced Collide@CERN at the ceremony for the Prix Ars Electronica, the Oscars of the digital media arts world, held this year in Brucknerhaus Concert Hall in Linz, Austria.

The digital artist who wins the Prix Ars Electronica Collide@CERN prize will spend two months at CERN developing a project and one month working with the Ars Electronica Futurelab team to realize it. A committee of judges will choose one artist per year for three years.

Understanding electron beam halos

Some physicists joke about electrons, saying that you cannot collimate them, you can only make them angry.

Collimation is the removal of low-intensity, high-amplitude particles from a particle beam, typically by absorption into a metal. These unwanted particles, which make up what’s known as the halo, could cause high backgrounds in collision data and wreak havoc on detector components.

Pavel Evtushenko, physicist at Jefferson Lab in the US, hopes his work will help create clean, tight electron beams for future electron-positron collision experiments such as those at the ILC. He and his colleagues in the laboratory’s Free Electron Laser Division are developing tools to perform improved beam diagnostics and beam dynamics studies for high-current electron linacs.

Third experiment sees hints of dark matter

From New Scientist, Sept. 8, 2011

A third experiment has detected tantalising signs of dark matter. The finding raises more questions than answers, however, as two other experiments have found no sign of the mysterious stuff, which is thought to create the gravity that holds spinning galaxies together, accounting for about 85 per cent of all matter in the universe.

The new result comes from an experiment called CRESST II, which uses a few dozen supercooled calcium tungstate crystals to hunt for dark matter from deep beneath the Gran Sasso mountain in Italy. When a particle hits one of the crystals, the crystal gives off a pulse of light, and sensitive thermometers gauge the energy of the collision.

The vast majority of hits come from garden-variety particles such as cosmic rays. These rain down on Earth from space in such large numbers that they strike CRESST II – which is shielded by a kilometre of rock – at a rate of about one per second. This shield should have little effect on dark-matter particles.

Bump hunters

Scientists look for evidence that two particles coalesce into a new kind of particle. Scientists expect that this particle would be observed by an unexpected bump in the expected signal (shown here in yellow).

A proton consists of smaller particles called partons. Parton is a generic term for the quarks and gluons that make up the proton. In the LHC, two protons collide. What this really means is that a parton from one proton is made to collide with a parton from the other one. Because the energy of a proton is randomly shared among its constituent partons, you can’t predict exactly how much energy will be involved in the actual collision. It’s a random process, with gentle collisions more likely than violent ones. This is, in part, because partons often have a small fraction of the proton’s energy. The low energy means collisions of low violence.

When you look at the collisions in detail, you see two different classes. In some instances the two partons just bounce off one another, similar to two billiard balls. However, occasionally the two partons will coalesce into a single object that exists for a while. The object then decays into two objects that eventually turn into the jets we observe in our detector. Jets look a bit like shotgun blasts of particles, and they represent the remnants of the objects created in the collision.

The rules of Quantum Chromodynamics govern how partons interact and make predictions on how many different types of interactions we should see (high energy vs. low energy and billiard-type vs. coalescence-type.) However, there are many new ideas predicting that collisions of certain energies are very much preferred. In these theories, two partons merge into a new kind of particle predicted by the theory. This particle then decays into jets similar to more ordinary collisions. If these particles exist, we’d see an excess of collisions at that particular energy.

CMS measured the energy of pairs of jets coming out of the collision. Unfortunately, no evidence was found to support these speculative ideas; however, as is often the case in measurements using the LHC, CMS was able to publish the most stringent limits to date.

—Don Lincoln

These physicists contributed to this analysis.

Part of USCMS governance involves elected positions. These physicists were in charge of the mechanics of the most recent election.